Put on a pair of latex gloves and sand the wood corbels with an 80-grit sanding block. Gently follow the grain of the wood and the carvings of the design as you sand. Repeat with 200-grit sandpaper, then 300-grit sandpaper.
Wipe down the corbels with a tack cloth. Dip your foam brush into the stain of your choice and cover the corbels with a generous coat of stain. Allow it to soak for 20 minutes.
Wipe off excess stain and repeat with another coat of stain, allowing the stain to penetrate for 20 minutes. Repeat with subsequent coats of stain if you want the corbels to have an even darker color.
Allow the stain to dry overnight. Dip your 3-inch nylon brush into a can of polyurethane and cover the corbels with a light coat. Allow the corbels to dry for 24 hours before hanging.